1. Field of the Invention
The invention is related to methods for the production of N-substituted (meth)acrylamides and is more particularly related to catalytic methods for the production of N-substituted (meth)acrylamides from (meth)acrylates and amines.
2. Description of Other Relevant Methods in the Field
It is well known that certain .beta.-aminopropionamide compounds can be made by reacting dialkylamine compounds with an acrylic acid or ester compound, as described in John G. Erickson's article, "The Preparation and Stabilities of Some .beta.-Dialkylaminopropionamides," J. Am. Chem. Soc. 74, 6281-82 (1952). The reference discloses that N,N-dialkyl-.beta.-dialkylaminopropionamides decompose, when heated at temperatures of about 125.degree.-215.degree. C., to corresponding dialkylamines and N,N-dialkylacrylamides and that the ease of such decomposition decreases from dibutylamine to dimethylamine derivatives. The observation of extensive polymerization of product substituted acrylamide when certain of the .beta.-dialkylaminopropionamides are heated is also described.
U.S. Pat. No. 2,451,436 to John G. Erickson teaches that N-alkylacrylamides can be prepared by subjecting an N-alkyl .beta.-alkylaminopropionamide, prepared by reacting 2 moles of an alkylamine or dialkylamine with an ester of acrylic or methacrylic acid, to elevated temperatures in the presence of a strong acid catalyst. The patent discloses that the acid catalyzed process results in the formation of the salt of the aminoamide which splits when heated into the alkyl amine salt and the N-alkylated acrylamide, the latter distilling off during heating.
U.S. Pat. No. 2,529,838 to John G. Erickson teaches that certain N,N-dialkylacrylamides are produced by heating a dialkylamine containing at least 5 carbon atoms per alkyl group with a monomeric acylic ester under superatmospheric pressure at temperatures between about 150.degree.-400.degree. C. The reference further teaches that dialkylamines containing fewer than 5 carbon atoms per alkyl group cannot be employed in the disclosed process.
However, these prior art processes have been found to be disadvantageous for the preparation of certain N-(aminoalkyl)acrylamide compounds inasmuch as they typically produce tarry or gummy reaction mixtures from which it is difficult to separate a good yield of pure product. For example, the employment of the acid catalyzed process described in U.S. Pat. No. 2,451,436 results in the production of alkylamino alkylacrylamides in salt form which are not volatile and, hence, cannot be readily recovered by distillation separation procedures. Moreover, the process described in U.S. Pat. No. 2,529,838 requires very high temperatures and superatmospheric pressures wherein the reactions are of a very long duration.
In view of these disadvantages, the abovedescribed processes have been considered inapplicable for the preparation of N-(tertiaryaminoalkyl)acrylamides and several alternative processes have been described. For example, U.S. Pat. No. 2,649,438 to Bruson, teaches that certain N-(tertiaryaminoalkyl)acrylamides can be prepared by reacting .beta.-propionlactone, ##STR1## with the desired tertiary amino diamine and distilling the reaction product under reduced pressure whereby dehydration readily occurs. The patent further teaches that other N-(tertiaryaminoalkyl)acrylamides can be obtained by reacting the appropriate acryloyl chloride with the desired tertiary amino diamine.
U.S. Pat. No. 3,652,671 to Barron describes a process for preparing N-(dialkylaminoalkyl)methacrylamides wherein the Michael adduct of methacrylic acid and an N,N-dialkylalkylenediamine; that is, the N-(dialkylaminoalkyl)-2-methyl- .beta.-alanine, is subjected to an elevated temperature of about 140.degree.-230.degree. C. which results in substantially complete rearrangement to the N-(dialkylaminoalkyl)methacrylamide product.
In view of the unavoidable secondary reactions at high temperatures, two-stage processes for the preparation of N-substituted acrylamides or methacrylamides have hitherto proved advantageous. In the process described in U.S. Pat. No. 3,878,247, one mole of an acrylate or methacrylate is reacted with 2 moles of an amine in the first reaction stage at a temperature below 200.degree.. The Michael addition and aminolysis proceed concomitantly, so that the corresponding .beta.-aminopropionamide or isobutyramide is obtained as an intermediate product. In the second reaction stage the amine added to the double bond is removed at temperatures above 200.degree., the substituted acrylamide or methacrylamide being obtained.
In order to avoid undesirable Michael addition, the process described in U.S. Pat. No. 2,719,175 involves the reaction of esters of acrylic or methacrylic acid with amines at 300.degree.-550.degree. C. in the gaseous phase in the presence of solid catalysts such as vanadium-aluminum oxides with contact times of a few seconds to form the corresponding substituted acrylamides or methacrylamides. The high reaction temperature favors uncontrolled decomposition and polymerization reactions, so that yields of at most 50% are obtained.
U.S. Pat. No. 4,206,143 (corresponding to British patent application No. 2,021,101A) reveals that dialkyl stannic oxide catalysts, such as dibutyl stannic oxide, are effective for the preparation of N-substituted-acrylamides and -methacrylamides from the reaction of an alkyl ester of acrylic or methacrylic acid with an aliphatic, cycloaliphatic or aromatic amine, which is a primary or secondary amine.
U.S. Pat. No 4,228,102 discloses that certain N-substituted acrylamides may be made by reacting an ester with an amine where the amine is present in an amount which is stoichiometrically deficient up to an amount which is in small stoichiometric excess with respect to the ester, without resorting to the use of a catalyst, but with heating and under pressure. However, the only example therein which is run under those conditions gave the poor yield of 32% to the amide. The other examples of that patent all employ an acidic catalyst to obtain a better yield.
Of particular interest is U.S. Pat. No. 4,321,411, issued on Mar. 23, 1982, which relates to a process for producing N-substituted acrylamide or methacrylamide comprising reacting an acrylic or methacrylic acid ester with an aliphatic or aromatic amine in liquid medium in the presence of a catalytic amount of an alkyltin alkoxide such as dibutyl dimethoxytin. This patent corresponds to British Patent Application No. 2,075,495A and Japanese Kokai No. 81-100,749.
Tin compounds have been used to catalyze a number of reactions. For example, German Pat. No. 1,005,947 (CA 54:14098c) reveals that the stability of plastics made from esters may be increased by reacting alcohols, carboxylic acids and the esters over organotin compounds such as BuSnO.sub.2 H, Bu.sub.2 SnO, Bu.sub.4 Sn, PhSnO.sub.2 H, PhSnOH, Ph.sub.4 Sn, Bu.sub.2 SnCl.sub.2 and (C.sub.12 H.sub.25).sub.2 SnO where Bu represents a butyl group and Ph represents a phenyl group. Organotin compounds are particularly useful for catalyzing esterifications. Hydroxybenzoic acid diesters were prepared by ester exchange of hydroxybenzoic acid esters with glycols in the presence of dialkyl tin compounds such as (C.sub.4 H.sub.9).sub.2 SnO.
Tin compounds are particularly useful as catalysts for the production of dialkylaminoethyl methacrylate. For example, Japanese Kokai No. 76-71,010 (CA 88:121898z) teaches that dialkyltin maleate, dialkyltin mercaptide and dialkylstannanediols are useful catalysts in this regard. Dibutyltin dimethoxide was found to be effective for the catalytic synthesis of dimethylaminoethyl methacrylate (DMAEMA), as described in Japanese Kokai No. 77-153,912 (CA 88:137169y). Further, compounds such as (C.sub.4 H.sub.9).sub.2 Sn(O.sub.2 CR).sub.2, where R is methyl or lauryl, are catalysts for the production of dialkylaminoethyl acrylates and methacrylates, as taught in Japanese Kokai No. 78-34,714 (CA 89:44410a).
U.S. Pat. No. 4,301,297 reveals that DMAEMA may be prepared in high yield by subjecting methyl methacrylate and dimethylaminoethanol to transesterification in the presence of di-n-octyl tin oxide as a catalyst. Compounds such as (C.sub.4 H.sub.9).sub.2 SnR.sub.2 (where R is hydrogen or --OCH.sub.3 or R.sub.2 is O.sub.2 CCH.dbd.CHCO.sub.2), (n--C.sub.8 H.sub.17).sub.2 Sno, (C.sub.6 H.sub.5).sub.3 SnOCH.sub.3 or (C.sub.4 H.sub.9).sub.3 SnO.sub.2 CCH.dbd.CHC--O.sub.2 Sn(C.sub.4 H.sub.9).sub.3) are effective in the manufacture of dialkylaminoethyl acrylates as seen in Japanese Kokai No. 78-144,522 (CA 90:169290p). In addition, U.S. Pat. No. 4,281,175 discloses that DMAEMA may be made via a number of tin catalysts such as tetrabutyltin, trioctyltin ethoxide, dibutyltin dimethoxide, dibutyltin dihydride, dibutyltin dilaurate, dibutyltin maleate, bis(tributyltin)oxide and bis(dibutylmethoxytin)oxide. See also Poller, R.C., et al., "Organotin Compounds as Transesterification Catalysts", Journal of Organometallic Chemistry, 173(1979) pp. C7-C8.
It would be desirable to have a process for the production of N-substituted acrylamides in high yield which could be performed in one step which did not employ corrosive, acidic catalysts or expensive, exotic catalysts or excessive temperature and pressure conditions, which have been problems with the previously described methods.